Dispersion of hematite suspensions with sodium polymethacrylate dispersants in alkaline medium

This article addresses the adsorption of sodium polymethacrylate (NaPMA) onto hematite powders in alkaline medium and the resulting stabilization of the suspensions. Both hematite and NaPMA are negatively charged under basic conditions such that pH is above the isoelectric point (IEP) of hematite. Adsorption isotherms, electrophoretic mobility, particle size, IR spectroscopy and rheological measurements were used to investigate the polymer–pigment interactions. It was found that adsorption of the anionic NaPMA polymer on hematite was still possible even at pH > IEP. Electrostatic interaction, chemical complexation at the surface or/and hydrogen bonding were suggested to be the dominant contributions to the adsorption process. The weaker adsorption at high pH was enough for preventing particles aggregation and ensuring an efficient stabilization of the suspensions. The viscosity measurements performed at pH close to the IEP also suggested that besides the electrostatic stabilization, the NaPMA polymers provided a steric stabilization. The steric effect was found larger with the polymers of higher molar mass.